Contact lens materials

ABSTRACT

A method for reducing the modulus of polymer silicone hydrogel compositions by employing monomeric polysiloxanes endcapped with trimethylsilyl to reduce the crosslinking density of the hydrogel. The synthesis consists of a single vessel acid catalyzed ring opening polymerization and may be employed to produce copolymers useful as hydrogel contact lens materials.

BACKGROUND OF THE INVENTION

[0001] The present invention generally relates to silicone hydrogelcompositions useful as biomedical devices, such as contact lenses andintraocular lenses.

[0002] Polymeric silicone materials have been used in a variety ofbiomedical applications, including, for example, in contact lenses andintraocular lenses. Such materials can generally be subdivided intohydrogels and non-hydrogels. Silicone hydrogels constitute crosslinkedpolymeric systems that can absorb and retain water in an equilibriumstate and generally have a water content greater than about 5 weightpercent and more commonly between about 10 to about 80 weight percent.Such materials are usually prepared by polymerizing a mixture containingat least one silicone-containing monomer and at least one hydrophilicmonomer. Either the silicone-containing monomer or the hydrophilicmonomer may function as a crosslinking agent (a crosslinker beingdefined as a monomer having multiple polymerizable functionalities) or aseparate crosslinker may be employed.

[0003] Silicone hydrogels combine the beneficial properties of hydrogelswith those of silicone-containing polymers (Kunzler and McGee, “ContactLens Materials”, Chemistry & Industry, pp. 651-655, 21 August 1995).Silicone hydrogels have been used to produce a contact lens thatcombines the high oxygen permeability of polydimethylsiloxane (PDMS)materials with the comfort, wetting and deposit resistance ofconventional non-ionic hydrogels.

[0004] Monomers that have been found to be particularly useful forpreparing silicone-containing contact lenses are described in U.S. Pat.Nos. 4,136,250; 4,153,641; 4,189,546; 4,208,506; 4,217,038; 4,277,595;4,327,203; 4,355,147; 4,740,533; 4,780,515; 5,034,461; 5,070,215;5,310,779; 5,346,976; 5,374,662; 5,358,995; 5,387,632; 5,420,324; and5,496,871.

[0005] U.S. Pat. No. 4,153,641 (Deichert et al) discloses contact lensesmade from poly(organosiloxane)monomers which are α,ω terminally bondedthrough a divalent hydrocarbon group to a polymerized activatedunsaturated group. Various hydrophobic silicone-containing prepolymerssuch as 1,3-bis(methacryloxyalkyl)-polysiloxanes were copolymerized withknown hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA).These materials were used to produce lenses which had a low watercontent and a high modulus (greater than 300 g/mm).

[0006] U.S. Pat. No. 5,358,995 (Lai et al) describes a silicone hydrogelwhich is comprised of an acrylic ester-capped polysiloxane prepolymer,polymerized with a bulky polysiloxanyalkyl(meth)acrylate monomer, and atleast one hydrophilic monomer. The acrylic ester-capped polysiloxaneprepolymer, commonly known as M₂D_(x) consists of two acrylic ester endgroups and “x” number of repeating dimethylsiloxane units. The preferredbulky polysiloxanyakyl(meth)acrylate monomers are TRIS-type(methacryloxypropyl tris(trimethylsiloxy)silane) with the hydrophilicmonomers being either acrylic- or vinyl-containing. While the propertiesof these lenses are acceptable, the modulus of these lenses can be high,which may result in damage to the epithelial layer and poor comfort.

[0007] Designing silicone based hydrogels utilizing M₂D_(x) as the baseprepolymer has mainly involved copolymerizing the prepolymer withhydrophilic monomers, such as dimethylacrylamide and N-vinylpyrrolidone.Silicone is hydrophobic and has poor compatibility with hydrophilicmonomers, especially when the M₂D_(x) prepolymer is of high molecularweight. Poor compatibility results in phase separated, opaque materials.This can be particularly problematic when preparing hydrogels to be usedas optically clear contact lenses.

[0008] Reducing the molecular weight of the M₂D_(x) prepolymer canimprove the incompatibility. Unfortunately, low molecular weight M₂D_(x)prepolymers typically result in hydrogels of high modulus. This is adirect result of the higher crosslink density of these low molecularweight M₂D_(x) based hydrogels.

[0009] In designing a low modulus silicone hydrogel based on lowmolecular weight M₂D_(x)prepolymers, one approach can be to use highconcentrations of hydrophilic monomers. The lower modulus for thesematerials is a result of the higher water content and lower cross-linkdensity. The major drawback of this approach is that the higher watercontent materials possess lower levels of oxygen permeability, due tothe lower concentration of silicone in these materials. The low levelsof oxygen permeability are not suitable for continuous wear contact lensapplication.

[0010] Another approach in the development of low modulus siliconehydrogels based on low molecular weight M₂D_(x)prepolymers is throughthe incorporation of the monomer methacryloxypropyltris(trimethylsiloxy)silane (“TRIS”). Higher concentrations of TRISresults in hydrogels of lower modulus, but lenses made with high TRISlevels overall tend not to perform well in clinical studies.

[0011] The development of low modulus hydrogels based on low molecularweight M₂D_(x)prepolymers may be accomplished through the addition ofsilicone macromonomers, such as those taught by Y. Kawakami in PolymerJournal, v. 14, p. 913, 1982. High levels of silicone macromonomer mayreduce the modulus by lowering the cross-link density of the resultanthydrogel without a significant reduction in oxygen permeability. Themajor disadvantage of this route is that the methacrylate based siliconemacromonomers are very difficult to synthesize. The synthesis ofsiloxane macromonomers requires several steps.

SUMMARY OF THE INVENTION

[0012] There remains a need for a contact lens material having the highoxygen permeablity of a polysiloxane-containing prepolymer, yet have amodulus low enough to be used as a contact lens. The approach taken inthis invention alters the silicone-containing monomer to affect thepolymer properties. By lowering the methacrylate functionality ofM₂D_(x), the cross-linking density is reduced. This can be done byremoving a percentage of the methacrylate groups on the end of theprepolymer.

[0013] These improved polymer silicone hydrogel compositions are formedfrom the polymerization product of a monomer mixture comprising asilicone prepolymer having the general formula:

[0014] wherein;

[0015] A is an activated unsaturated radical;

[0016] A′ is either an activated unsaturated radical or an alkyl group;

[0017] R₁-R₁₀ are independently an alkyl, fluoroalkyl, alcohol, ether,or fluoroether group having 1-10 carbons, or an aromatic group having6-18 carbons;

[0018] m, n, and p are independently 0 to 200, m+n+p being from about 15to 200;

[0019] a is 1 to 10; and

[0020] b is 0 to 10,

[0021] wherein the silicone prepolymer is prepared by the reaction ofdimethacrylate disiloxane (M) and cyclic siloxane (D) in the presence ofan catalyst, the improvement comprising adding at least one disiloxane(T₂) having the fomula:

[0022] wherein R₁₁-R₁₆ are independently an alkyl group having 1-5carbons, to the reaction mixture used to form the silicone prepolymer.

[0023] In particular, this invention is directed to preparing a M₂D_(x)based prepolymer that is endcapped with trimethylsilyl(TMS) as shown informula II:

[0024] wherein m+n+p is 15 to 200.

[0025] Note that prepolymers of formula II are a species of formula Iwherein b is zero and R₉,R₁₀ and A′ are methyl groups.

[0026] Applicants have found that the above preparation of making theprepolymer is especially effective in improving the flexibility ofpolymer silicone materials and hence lowering the modulus of siliconehydrogel copolymers, in contrast to previous siloxane compounds whichwere methacrylate endcapped and not endcapped with trimethyl silyl. Thesynthesis of the M₂D_(x), TMS-endcapped prepolymer is easy, requiringfewer steps and components than previous methods.

[0027] The hydrogel material is especially useful in biomedical devicessuch as soft contact lenses, intraocular lenses, heart valves and otherprostheses.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] This invention describes a novel approach to the design of lowmodulus silicone hydrogels based on M₂D_(x) prepolymers. The M₂D_(x)prepolymers of this invention contain a “built-in” modulus reducingfunctionality: a trimethylsilyl(TMS) endcap. Increasing theconcentration of the TMS endcap (or reducing the concentration of themethacrylate cap) results in lower modulus, transparent siliconehydrogels without a reduction in water transport or oxygen permeability.

[0029] These improved polymer silicone hydrogel compositions are formedfrom the polymerization product of a monomer mixture comprising asilicone prepolymer having the general formula:

[0030] wherein;

[0031] A is an activated unsaturated radical;

[0032] A′ is either an activated unsaturated radical or an alkyl group;

[0033] R₁-R₁₀ are independently an alkyl, fluoroalkyl, alcohol, ether,or fluoroether group having 1-10 carbons, or an aromatic group having6-18 carbons;

[0034] m, n, and p are independently 0 to 200, m+n+p being from about 15to 200;

[0035] a is 1 to 10; and

[0036] bis Oto 10,

[0037] wherein the silicone prepolymer is prepared by the reaction ofdimethacrylate disiloxane (M₂) and cyclic siloxane (D) in the presenceof an catalyst, the improvement comprising adding at least onedisiloxane (T₂) having the formula:

[0038] wherein R₁₁-R₁₆ are independently an alkyl group having 1-5carbons, to the reaction mixture used to form the silicone prepolymer.

[0039] With respect to A, A′ of formula I, the term “activated is usedto describe unsaturated groups which include at least one substituentwhich facilitates free radical polymerization, preferably anethylenically unsaturated radical. This includes esters or amides ofacrylic or methacrylic acid represented by the general formula:

[0040] wherein X is preferably hydrogen or methyl but may include othergroups, e.g., cyano, and Y represents —O—, —S—, or —NH—, but ispreferably —O—. Examples of other suitable activated unsaturated groupsinclude vinyl carbonates, vinyl carbamates, fumarates, fumaramides,maleates, acrylonitryl, vinyl ether and styrl.

[0041] Dimethacrylate disiloxane (M₂) is represented by the generalformula:

[0042] Cyclic siloxane (D) may be any cyclical compound and substituteanalogs containing at least 3 silicone-oxygen groups. Examples include1,1,3,3-tetramethyl-1,3-disila-2-oxacyclopentane,hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane or mixturesthereof. The preferred D is octamethylcyclotetrasiloxane (D₄).

[0043] The preferred T₂ is hexamethyl disiloxane and is represented bythe following formula:

[0044] The catalyst used must be able to cleave Si—O bonds. Those agentsinclude acid clays, hydrogen fluoride acid, HCl—FeCl3 (hydrochloricacid-iron(II) chloride complex), concentrated sulfuric acid, andtrifluoromethane sulfonic (triflic) acid. The preferred acids areconcentrated sulfuric acid and triflic acid.

[0045] The present invention contemplates polymerizing polysiloxaneprepolymer mixture with bulky polysiloxanylalkyl(meth)acrylate monomersand at least one hydrophilic monomer. The polysiloxane prepolymersutilized in this invention are those having m+n+p equal to about 15 to200 repeating dimethylsiloxane units. Preferred polysiloxane prepolymersare those having about 25 to about 50 repeating dimethylsiloxane units.More preferred polysiloxane prepolymers are those in which there are 25repeating dimethylsiloxane units.

[0046] It is preferred that the total concentration of the prepolymer isendcapped with 1 to 70 mole % trialkylsilyl, preferably 25 to 50 mole %trialkylsilyl and more preferably 40 to 50 mole % trialkylsilyl. Thus,“prepolymer” as used herein denotes a compound having formulae (I) and(II):

[0047] These M₂D_(x), TMS-endcapped prepolymers are extremely easy tosynthesize. The synthesis consists of an acid catalyzed, ring openingpolymerization conducted in a single vessel. The cyclic siloxanes (D),endcapping agents (M₂) and disiloxanes (T₂) are simply added to areaction vessel together with a suitable catalyst and stirred at roomtemperature for a period of time.

[0048] Silicone hydrogels of this invention are crosslinked polymericsystems that can absorb and retain water in an equilibrium state. Thesepolymeric systems are based on at least one silicone-containing monomerand at least one hydrophilic monomer. Preferably, the silicone hydrogelsof this invention are formed by polymerizing a monomer which comprisesthe prepolymer mixture of this invention, a second unsaturatedsilicone-containing monomer and at least one hydrophilic monomer. Morepreferably, the second unsaturated silicone-containing monomer mayinclude monofunctional silicone-containing monomers. Most preferably,the monofunctional silicone-containing monomer is at least one member ofthe group consisting of bulky polysiloxanylalkyl(meth)acrylic monomersare represented by Formula (III):

[0049] wherein:

[0050] X denotes —COO—, —CONR⁴—, —OCOO—, or —OCONR⁴— where each where R⁴is independently H or lower alkyl; R³ denotes hydrogen or methyl; h is 1to 10; and each R² independently denotes a lower alkyl radical, a phenylradical or a radical of the formula

—Si(R⁵)₃

[0051] wherein each R⁵ is independently a lower alkyl radical or aphenyl radical.

[0052] Such bulky monomers specifically include methacryloxypropyltris(trimethylsiloxy)silane (“TRIS”), pentamethyldisiloxanylmethylmethacrylate, tris(trimethylsiloxy)methacryloxy propylsilane,phenyltetramethyl-disiloxanylethyl acrylate,methyldi(trimethylsiloxy)methacryloxymethyl silane,3-[tris(trimethylsiloxy)silyl]propyl vinyl carbamate,3-[tris(trimethylsiloxy)silyl]propyl allyl carbamate, and3-[tris(trimethylsiloxy)silyl]propyl vinyl carbonate.

[0053] Preferred hydrophilic monomers may be either acrylic- orvinyl-containing. The term “vinyl-type” or vinyl-containing” monomersrefers to monomers containing the vinyl grouping (CH₂═CHR) and aregenerally reactive. Such hydrophilic vinyl-containing monomers are knownto polymerize relatively easily. Acrylic-containing monomers are thosemonomers containing the acrylic group (CH₂═CRCOX) wherein R═H or CH₃ andX═O or NH, which are also known to polymerize readily.

[0054] Examples of suitable hydrophilic monomers include: unsaturatedcarboxylic acids, such as methacrylic and acrylic acids; acrylicsubstituted alcohols, such as 2-hydroxyethyl methacrylate and2-hydroxyethylacrylate; vinyl lactams, such as N-vinyl pyrrolidone; andacrylamides, such as methacrylamide with N,N-diethyl acrylamide (DMA)being the most preferred. Other monomers include glycerol methacrylateand 2-hydroxyethyl methacrylamide.

[0055] Silicone hydrogels of this invention are typically formed bypolymerizing a monomer mixture comprising: about 10 to about 90 weightpercent of a prepolymer, preferably 20 to 70 weight percent of aprepolymer, more preferably 20 to 50 weight percent, comprised ofmonomers represented by formula I and formula II wherein the totalconcentration of the prepolymer is endcapped with about 1 to about 70mole % trimethylsilyl, preferably about 25 to about 50 mole %trimethylsilyl, more preferably about 40 to about 50 mole %trimethylsilyl; about 10 to about 50 weight percent of a monofunctionalethylenically unsaturated silicone-containing monomer, more preferablyabout 20 to about 50 weight percent of a monofunctional ethylenicallyunsaturated silicone-containing monomer, more preferably about 20 toabout 40 weight percent of a monofunctional ethylenically unsaturatedsilicone-containing monomer, and about 5 to about 70 weight percent of ahydrophilic monomer, preferably 10 to about 50 weight percent of ahydrophilic monomer, more preferably about 20 to about 40 weight percentof a hydrophilic monomer. An example of a silicone hydrogel made fromthis invention may have about 20 parts of a prepolymer that is endcappedwith 50 mole % TMS, about 35 parts of a hydrophilic monomer, about 25parts of an monofunctional ethylenically unsaturated silicone-containingmonomer. Other components, such as a diluent may be added and arediscussed below.

[0056] The monomer mixture of the present invention may includeadditional constituents such as UV-absorbing agents, internal wettingagents, hydrophilic monomeric units, toughening agents, or colorantssuch as those known in the contact lens art.

[0057] Conventional curing methods in polymerizing ethylenicallyunsaturated compounds such as UV polymerization, thermal polymerization,or combinations thereof, can be used to cast these monomer mixtures.Representative free radical thermal polymerization initiators can beorganic peroxides and are usually present in the concentration of about0.01 to 1 percent by weight of the total monomer mixture. RepresentativeUV initiators are known in the field such as, benzoin methyl ether,benzoin ethyl ether, 1164, 2273, 1116, 2959, 3331 (EM Industries) andIrgacure 651 and 184 (Ciba-Geigy). In the preferred embodiment, Darocur1173 is the UV initiator.

[0058] Polymerization of the prepolymer of this invention with othercopolymers is generally performed in the presence of a diluent. Thediluent is generally removed after polymerization and replaced withwater in extraction and hydration protocols well known to those skilledin the art. Representative diluents are diols, alcohols, alcohol/watermixtures, ethyleneglycol, glycerine, liquid polyethyleneglycol, lowmolecular weight linear polyhydroxyethylmethacrylates, glycol esters oflactic acid, formamides, ketones, dialkylsulfoxides, butyl carbitol, andthe like. Preferred diluents include hexanol and nonanol.

[0059] It is also possible to perform the polymerization in the absenceof diluent to produce a xerogel. These xerogels may then be hydrated toform hydrogels as is well known in the art.

[0060] The monomer mixture may include a tinting agent, defined as anagent that, when incorporated in the final lens, imparts some degree ofcolor to the lens. Conventional tinting agents are known in the art,including non-polymerizable agents, or polymerizable agents that includean activated unsaturated group that is reactive with the lens-formingmonomers. One preferred example of this latter class is the compound1,4-bis(4-(2-methacryloxyethyl)phenylamino)anthraquinone, a bluevisibility-tinting agent disclosed in U.S. Pat. No. 4,997,897(Melpolder).

[0061] The monomer mixture may also include a UV-absorbing agent,defined as an agent that reduces light in the general region of 200 to400 nm. Representative polymerizable UV absorbing materials for contactlens applications are described in U.S. Pat. No. 4,304,895 (Loshaek),U.S. Pat. No. 4,528,311 (Beard et al), U.S. Pat. No. 4,716,234 (Dunks etal), U.S. Pat. No. 4,719,248 (Barnbury et al), U.S. Pat. No. 3,159,646(Manneus et al) and U.S. Pat. No. 3,761,272 (Manneus et al). Examples ofUV-absorbing compounds include the benzotriazoles and benzophenones.

[0062] Various techniques for molding hydrogel polymer mixtures intocontact lenses are known in the art, including spin casting and staticcast molding. Spin casting processes are disclosed in U.S. Pat. Nos.3,408,429 and 3,496,254. Static cast molding involves charging aquantity of polymerizable monomeric mixture to a mold assembly, andcuring the monomeric mixture while retained in the mold assembly to forma lens, for example, by free radical polymerization of the monomericmixture. Examples of free radical reaction techniques to cure the lensmaterial include thermal radiation, infrared radiation, electron beamradiation, gamma radiation, ultraviolet (UV) radiation, and the like;combinations of such techniques may be used. The mold assembly defines amold cavity for casting the lens, including an anterior mold fordefining the anterior lens surface and a posterior mold for defining theposterior lens surface.

[0063] U.S. Pat. No. 5,271,875 describes a static cast molding methodthat permits molding of a finished lens in a mold cavity defined by aposterior mold and an anterior mold.

[0064] The hydrogels of the present invention are oxygen transporting,hydrolytically stable, biologically inert and transparent. When used inthe formation of contact lenses, it is preferred that the subjecthydrogels have water contents of from about 5 to about 70 weightpercent. More preferred is about 25 to about 50 weight percent.Furthermore, it is preferred that such hydrogels have a modulus fromabout 20 g/mm² to about 200 g/mm², and more preferably from about 75g/mm² to about 175 g/mm².

[0065] As stated previously, the M₂D_(x), TMS-endcapped prepolymers areextremely easy to synthesize. There are fewer steps and componentsneeded than found in previously known methods. This reduces the cost andtime necessary for producing the hydrogels or contact lenses.

[0066] As an illustration of the present invention, several examples areprovided below. These examples serve only to further illustrate aspectsof the invention and should not be construed as limiting the invention.

EXAMPLE 1 Preparation of 1,3-bis(4-methacryloyloxybutyl)tetramethyldisiloxane (M₂)

[0067] To a 5 liter four neck resin flask equipped with a mechanicalstirrer, Dean-Stark trap, heating mantle, water cooled condenser andthermometer was added 1,1-dimethyl-1-sila-2-oxacyclohexane (521 g, 4.0mol), methacrylic acid (361 g, 4.2 mol), and concentrated sulfuric acid(25.5 g). To the reaction mixture was then added 1 L of cyclohexane andhydroquinone (0.95 g, 8.6 mmol) as a polymerization inhibitor. Thereaction mixture was heated to reflux for five hours during which time28 mL of water was collected. The reaction mixture was then cooled,divided and passed through two chromatography columns filled with 1 kgof alumina (packed using cyclohexane as eluent). The cyclohexane wasremoved using a rotary evaporator and the resultant M₂ was placed undervacuum (0.2 mm Hg) for one hour at 80° C. (yield, 80%; purity by gaschromatography, 96%).

EXAMPLE 2 Synthesis of Methacrylate End-Capped Poly Dimethylsiloxane(M₂D₂₅)

[0068] To a 1,000-mL round-bottom flask under dry nitrogen was addedoctamethylcyclotetrasiloxane (D₄) (371.0 g, 1.25 mol) and M₂ (27.7 g,0.7 mol). Triflic acid (0.25%, 1.25 g, 8.3 mmol) was added as initiator.The reaction mixture was stirred for 24 hours with vigorous stirring atroom temperature. Sodium bicarbonate (10 g, 0.119 mol) was then addedand the reaction mixture was again stirred for 24 hours. The resultantsolution was filtered through a 0.3-μm-pore-size Teflon® filter. Thefiltered solution was vacuum stripped and placed under vacuum (>0.1 mmHg) at 50° C. to remove the unreacted silicone cyclics. The resultingsilicone hydride-functionalized siloxane was a viscous, clear fluid:yield, 70%.

COMPARATIVE EXAMPLES 3-16 Formulations of the Hydrogel with VaryingRatios

[0069] Formulations comprising the following substituents were prepared:α,ω-Bis(methacryloxyalkyl)polysiloxane (M₂D₂₅), methacryloxypropyltris(trimethylsiloxy)silane (“TRIS”) and N,N-dimethyl acrylamide (DMA).Each formulation contained a constant amount of hexanol as solvent (20parts) and Darocur-1173 as a photoinitiator (0.5 parts). Allformulations were UV-cured between two glass plates for two (2) hours atroom temperature. The resultant films were isolated, followed byextraction with ethanol for sixteen (16) hours and boiling waterhydration for four (4) hours, then placed in borate buffered saline. Theratios of the various substituents were varied, with the resultingproperties noted.

[0070] The water contents and isopropanol extractables for films castaccording to the procedures set forth above were measuredgravimetrically. The tensile and tear properties were determined inbuffered saline, according to the standard ASTM procedures 1708 and 1938respectively. The oxygen permeabilities were determined by polargraphicmethods taking the edge effect into consideration. (See Fatt, Rasson andMelpolder, Int'l Contact Lens Clinic, v. 14, 389 (1987)). TABLE 1 Filmsprepared using M₂D₂₅ endcapped with 0% mole trimethylsilyl DMA TRISM₂D₂₅ DK H₂O Weight Modulus H₂O Example (parts) (parts) (parts)(Barrers) (%) Loss (%) (g/mm²) trans 3 20.00 39.50 20.00 179.00 11.6117.83 181 1.05 4 23.95 33.10 22.45 131.60 17.94 19.25 223 14.91 5 35.0024.50 20.00 85.00 32.70 21.19 212 79.96 6 35.00 20.00 24.50 196.00 32.1921.48 290 91.35 7 20.00 29.50 30.00 181.90 10.65 17.72 306 9.03 8 20.0039.50 20.00 189.30 10.12 18.81 204 4.53 9 20.00 34.50 25.00 139.40 11.5618.65 238 6.93 10 35.00 20.00 24.50 91.10 32.21 19.83 305 70.4 11 29.5020.00 30.00 129.40 23.67 19.93 355 45.21 12 24.75 24.75 30.00 120.2017.36 21.80 327 19.46 13 35.00 24.50 20.00 85.40 34.70 21.35 219 74.0714 20.00 29.50 30.00 201.90 12.19 21.10 314 4.59 15 31.45 23.35 24.70113.30 29.55 21.85 274 51.83 16 27.90 26.70 24.90 125.20 23.42 21.55 26022.25

[0071] Silicone hydrogel prepared with the above components producefilms with generally high gen permeability. It is noted that the modulusof some of these films was too high for contact lens application.

EXAMPLES 17-30 Films Prepared with M₂D₂₅ Endcapped with 10% moletrimethylsilyl

[0072] This prepolymer was prepared by same procedure as above exceptthat for the following amounts: M₂ 9.08 grams, D₄ 40.57 grams, T₂(hexamethyldisiloxane) 0.35 grams and triflic acid 0.125 grams. TABLE 2Films prepared using M₂D₂₅ endcapped with 10% mole trimethylsilyl DMATRIS M₂D₂₅ DK H₂O Weight Modulus H₂O Example (parts) (parts) (parts)(Barrers) (%) Loss (%) (g/mm²) trans 17 20.00 39.50 20.00 200.00 11.6917.42 163 1.16 18 23.95 33.10 22.45 160.40 18.04 19.47 191 9.53 19 35.0024.50 20.00 80.40 32.62 19.48 179 91.35 20 35.00 20.00 24.50 77.80 33.8924.61 263 2.68 21 20.00 29.50 30.00 187.30 10.65 17.72 246 2.79 22 20.0039.50 20.00 208.00 9.97 18.70 164 6.04 23 20.00 34.50 25.00 198.60 11.9319.15 215 7.72 24 35.00 20.00 24.50 84.50 31.80 19.27 250 90.99 25 29.5020.00 30.00 120.20 23.33 19.19 329 40.44 26 24.75 24.75 30.00 164.1017.43 19.55 275 20.54 27 35.00 24.50 20.00 75.80 34.06 21.03 190 79.8628 20.00 29.50 30.00 158.30 11.88 20.16 284 2.91 29 31.45 23.35 24.70102.70 27.03 22.14 272 59.79 30 27.90 26.70 24.90 119.70 22.97 21.11 23222.55

[0073] Films containing M₂D₂₅ endcapped with 10% mole trimethylsilylshowed a reduction in modulus as compared to Examples 3-16. The oxygenpermeability was acceptable.

EXAMPLES 31-44 Films Prepared with M₂D₂₅ endcapped with 25% moletrimethylsilyl

[0074] This prepolymer was prepared by same procedure as above exceptthat for the following amounts: M₂ 8.98 grams, D₄ 40.14 grams, T₂ 0.88grams and triflic acid 0.125 grams. TABLE 3 Films prepared using M₂D₂₅endcapped with 25% mole trimethylsilyl DMA TRIS M₂D₂₅ DK H₂O WeightModulus H₂O Example (parts) (parts) (parts) (Barrers) (%) Loss (%)(g/mm²) trans 31 20.00 39.50 20.00 126.60 12.17 18.34 137 0.65 32 23.9533.10 22.45 134.40 18.21 18.68 158 7.47 33 35.00 24.50 20.00 92.50 33.6718.84 161 69.93 34 35.00 20.00 24.50 79.00 35.04 21.71 227 90.15 3520.00 29.50 30.00 67.30 12.44 24.39 250 1.96 36 20.00 39.50 20.00 156.509.56 20.23 139 4.53 37 20.00 34.50 25.00 169.90 11.08 18.77 181 8.43 3835.00 20.00 24.50 87.40 32.65 20.96 232 91.11 39 29.50 20.00 30.00129.50 25.59 20.36 282 68.92 40 24.75 24.75 30.00 201.10 18.96 20.84 24117.73 41 35.00 24.50 20.00 87.50 34.89 21.93 155 89.85 42 20.00 29.5030.00 126.70 12.80 21.54 165 2.57 43 31.45 23.35 24.70 92.80 29.32 21.91209 59.53 44 27.90 26.70 24.90 142.00 24.58 21.56 197 29.18

[0075] Films made with M₂D₂₅ endcapped with 25% mole trimethylsilylshowed a decrease modulus as compared to Examples 17-30.

EXAMPLES 45-46

[0076] Films prepared with M₂D₂₅ endcapped with 40% mole trimethylsilylThis prepolymer was prepared by same procedure as above except that forthe following amounts: M₂ 8.89 grams, D₄ 39.72 grams, T₂ 1.39 grams andtriflic acid 0.125 grams. TABLE 4 Films prepared using M₂D₂₅ endcappedwith 40% mole trimethylsilyl DMA NVP TRIS M₂D₂₅ DK H₂O Weight ModulusExample (parts) (parts) (parts) (parts) (Barrers) (%) Loss (%) (g/mm²)45 17.50 17.50 24.50 20.00 72.90 35.05 32.50 126 46 17.50 17.50 24.5020.00 76.30 36.03 23.81 120

[0077] Films containing M₂D₂₅ endcapped with 40% mole trimethylsilylshowed a reduction in modulus as compared to Examples 31-44.

EXAMPLES 47-48

[0078] Films prepared with M₂D₂₅ endcapped with 50% mole trimethylsilylThis prepolymer was prepared by same procedure as above except that forthe following amounts: M₂ 8.82 grams, D₄ 39.45 grams, T₂ 1.73 grams andtriflic acid 0.125 grams. TABLE 5 Films prepared using M₂D₂₅ endcappedwith 50% mole trimethylsilyl DMA NVP TRIS M₂D₂₅ DK H₂O Weight ModulusExample (parts) (parts) (parts) (parts) (Barrers) (%) Loss (%) (g/mm²)47 17.50 17.50 24.50 20.00 65.30 36.55 24.33 109 48 17.50 17.50 24.5020.00 76.30 35.53 24.86 103

[0079] Films containing M₂D₂₅ endcapped with 50% mole trimethylsilylshowed a reduction in modulus as compared to Examples 45, 46.

[0080] Many other modification and variations of the present inventionare possible to the skilled practitioner in the field in light of theteachings herein. It is therefore understood that, within the scope ofthe claims, the present invention can be practiced other than as hereinspecifically described.

We claim:
 1. In a hydrogel formed from the polymerization product of amonomer mixture comprising silicone prepolymers having the genericformula:

wherein; A is an activated unsaturated radical; A′ is either anactivated unsaturated radical or an alkyl group; R₁-R₁₀ areindependently an alkyl, fluoroalkyl, alcohol, ether, or fluoroethergroup having 1-10 carbons, or an aromatic group having 6-18 carbons; m,n, and p are independently 0 to 200, m+n+p being from about 15 to 200; ais 1 to 10; and b is 0 to 10, wherein the silicone prepolymer isprepared by the reaction of a cyclic siloxane (D) and a dimethacrylatedisiloxane (M₂) in the presence of a catalyst, the improvementcomprising adding at least one disiloxane (T₂) having the formula:

wherein R₁₁-R₁₆ are independently an alkyl group having 1-5 carbons, tothe reaction mixture used to form the silicone prepolymer.
 2. The methodof claim 1, wherein crosslinking density of said hydrogel decreases asthe amount of said T₂ increases.
 3. The method of claim 1, whereindimethacrylate disiloxane (M₂) is represented by the formula:


4. The method of claim 1, wherein m+n+p of said polysiloxane prepolymeris within a range of about 25 to
 50. 5. The method of claim 4, whereinm+n+p of said polysiloxane prepolymer is about
 25. 6. The method ofclaim 1, wherein said polysiloxane prepolymer is endcapped with 1 to 70mole % trimethylsilyl.
 7. The method of claim 6, wherein said prepolymeris endcapped within the range of 25 to 50 mole % trimethylsilyl.
 8. Themethod of claim 7, wherein said prepolymer is endcapped within the rangeof 40 to 50 mole % trimethylsilyl.
 9. The method of claim 1, whereinm+n+p of said polysiloxane prepolymer is about 25 and endcapped withabout 50 mole % trimethylsilyl.
 10. The method of claim 1, wherein D isoctamethylcyclotetrasiloxane.
 11. The method of claim 1, wherein D is1,1,3,3-tetramethyl-1,3-disila-2-oxacyclopentane.
 12. The method ofclaim 1, wherein D is hexamethylcyclotrisiloxane.
 13. The method ofclaim 1, wherein said catalyst is trifluoromethane sulfonic acid. 14.The method of claim 1, wherein T₂ is hexamethyl disiloxane.
 15. Themethod of claim 1, wherein said monomer mixture further comprises ahydrophilic monomer.
 16. The method of claim 15, wherein saidhydrophilic monomer is an acrylic-containing monomer.
 17. The method ofclaim 16, wherein said hydrophilic monomer is N,N-dimethyl acrylamide.18. The method of claim 15, wherein said hydrophilic monomer is avinyl-containing monomer.
 19. The method of claim 18, wherein saidhydrophilic monomer is N-vinyl pyrrolidone.
 20. The method of claim 15,still further comprising a monofunctional, ethylenically unsaturatedsilicone-containing monomer.
 21. The method of claim 20, wherein saidmonofunctional, ethylenically unsaturated silicone-containing monomer isrepresented by the formula:

wherein: X denotes —COO—, —CONR⁴—, —OCOO—, or —OCONR⁴— where each whereR⁴ is independently H or lower alkyl; R³ denotes hydrogen or methyl; his 1 to 10; and each R² independently denotes a lower alkyl radical, aphenyl radical or a radical of the formula —Si(R⁵)₃ wherein each R⁵ isindependently a lower alkyl radical or a phenyl radical.
 22. The methodof claim 1, wherein said monomer mixture further comprises a UVinitiator.
 23. The method of claim 22, wherein said UV initiator isDarocur
 1173. 24. The method of claim 1, wherein said monomer mixturefurther comprises a diluent.
 25. The method of claim 24, wherein saiddiluent is hexanol.
 26. A silicone-containing, hydrogel formed from thepolymerization product of a monomer mixture comprising: (a) polysiloxaneprepolymers represented by the formula:

wherein; A is an acitvated unsaturated radical; A′ is either anactivated unsaturated radical or an alkyl group; R₁-R₁₀ areindependently an alkyl, fluoroalkyl, alcohol, ether, or fluoroethergroup having 1-10 carbons, or an aromatic group having 6-18 carbons; m,n, and p are independently 0 to 200, m+n+p being from about 23 to 200; ais 1 to 10; and b is 0 to 10 wherein the silicone prepolymer is preparedby the reaction of dimethacrylate disiloxane (M₂) and cyclic siloxane(D) in the presence of a catalyst, the improvement comprising adding atleast one disiloxane (T₂) having the formula:

wherein R₁₁-R₁₆ are independently an alkyl group having 1-5 carbons, tothe reaction mixture used to form the silicone prepolymer, (b) ahydrophilic monomer, and (c) a monofunctional, ethylenically unsaturatedsilicone-containing monomer.
 27. The hydrogel of claim 26, wherein m+n+pof said polysiloxane prepolymer is within the range of 25 to
 50. 28. Thehydrogel of claim 27, wherein m+n+p of said polysiloxane prepolymer isabout
 25. 29. The hydrogel of claim 26, wherein said polysiloxaneprepolymer is endcapped within the range of 1 to 70 mole %trimethylsilyl.
 30. The hydrogel of claim 29, wherein said prepolymer isendcapped within the range of 25 to 50 mole % trimethylsilyl.
 31. Thehydrogel of claim 30, wherein said prepolymer is endcapped within therange of 40 to 50 mole % trimethylsilyl.
 32. The hydrogel of claim 26,wherein m+n+p of said polysiloxane prepolymer is about 25 and endcappedwith about 50 mole % trimethylsilyl.
 33. The hydrogel of claim 26,wherein T₂ is hexamethyl disiloxane.
 34. The hydrogel of claim 26,wherein said hydrophilic monomer is an acrylic-containing monomer. 35.The hydrogel of claim 34, wherein said hydrophilic monomer isN,N-dimethyl acrylamide.
 36. The hydrogel of claim 26, wherein saidhydrophilic monomer is a vinyl-containing monomer.
 37. The hydrogel ofclaim 36, wherein said hydrophilic monomer is N-vinyl pyrrolidone. 38.The hydrogel of claim 26, wherein said monofunctional, ethylenicallyunsaturated silicone-containing monomer is represented by the formula:

wherein: X denotes —COO—, —CONR⁴—, —OCOO—, or —OCONR⁴— where each whereR⁴ is independently H or lower alkyl; R³ denotes hydrogen or methyl; his 1 to 10; and each R² independently denotes a lower alkyl radical, aphenyl radical or a radical of the formula —Si(R⁵)₃ wherein each R⁵ isindependently a lower alkyl radical or a phenyl radical.
 39. Thehydrogel of claim 26, wherein the monomer mixture further comprises a UVinitiator.
 40. The hydrogel of claim 39, wherein said UV initiator isDarocur
 1173. 41. The hydrogel of claim 26, wherein the monomer mixturefurther comprises a diluent.
 42. The hydrogel of claim 41, wherein thediluent is hexanol.
 43. A contact lens comprising the hydrogel of claim26.
 44. An intraocular lens comprising the hydrogel of claim 26.